The invention relates to a method for operating an electric high voltage energy storage device, as well as an energy supply device for a hybrid vehicle.
Currently it is known to operate high voltage accumulators—in particular, high voltage accumulators, based on lithium ion technology, with a nominal voltage greater than or equal to 60 V—within a predefined fixed operating range. This operating range is usually chosen in such a way that, on the one hand, a defined cold start (for example, a start of the internal combustion engine at −25° C.) has to be possible at any time (lower state of charge limit/minimum storage capacity) and that, on the other hand, there is (in the upward direction) adequate storage capacity (upper state of charge limit/maximum storage capacity) in order to be able to use the energy accumulator for brake energy regeneration.
The object of the invention is to provide a method for operating an electric high voltage energy storage device (in particular a high voltage energy storage device for supplying an electric drive motor of a hybrid vehicle), so that the result is a smaller design of said electric drive motor and so that slower ageing of the energy storage device is guaranteed. Furthermore, the object is to provide an energy supply device which comprises such a high voltage energy storage device, so that the size of the corresponding package is reduced and at the same time slower ageing of the energy storage device is achieved.
The invention is based on the knowledge that high voltage energy Accumulators—in particular, those that are designed on the basis of lithium ion Technology—age comparatively faster at high temperatures and/or at high states of charge than at lower temperatures and/or lower states of charge. Furthermore, as the ageing process of such energy accumulators increases, their performance decreases. In order to counteract these phenomena, a method and/or an energy supply device is proposed in accordance with the invention.
In the present invention, an electric high voltage energy storage device of a hybrid vehicle with an electric drive motor (in particular, a hybrid vehicle that can be operated by electrical means and/or by an internal combustion engine) is operated in such a manner that a predetermined working range of the high voltage energy storage device that is defined by an upper and a lower limit is shifted as a function of the vehicle operating parameters and/or as a function of the vehicle environmental parameters. The electric drive motor is defined for the purpose of the invention as an electric motor, by which it is possible to generate the torque that acts on the drive wheels.
The working range is shifted advantageously by shifting the upper and/or lower limit of the predetermined working range. In particular, the shift of the working range takes place by shifting the lower limit of the working range. In an additional advantageous design the entire breadth of the working range (the distance between the upper and the lower limit) is retained and shifted in its entirety. That is, the upper and the lower limits are shifted by the same degree (and/or the same amount) in the same direction.
Preferred vehicle operating parameters are for the purpose of the invention those parameters that correlate with the state of ageing of the energy storage device-in particular the cumulative operation period of the energy storage device (optionally weighted as a function of the states of charge that occur over the total operating time). An additional vehicle operating parameter that can be used as an alternative or as an addition in order to determine the state of ageing of the energy storage device is the energy throughput (energy throughput per defined period of time) through the energy accumulator. Furthermore, it is possible to determine the state of ageing by a computational algorithm, in particular as a function of the measurable variables of the battery, like the current, the cell voltages and the temperature. Preferred vehicle environmental parameters that can be mentioned are those parameters that correlate with the ambient air and/or the outside air temperature of the energy storage device or the motor vehicle. In this case special mention must be given to the vehicle ambient temperature, which is measured over a predetermined period of time, and/or its minimum temperature. It is advantageous to measure continuously the predetermined temperature variable (for example, the outside temperature) and to find as a function thereof a minimum temperature, on which an additional calculation is to be based. This so-called seasonal temperature may be used to differentiate between at least two temporal operating ranges (differing significantly in their lowest temperature)—for example, summer mode and winter mode—and to operate, as a function of the determined seasonal temperature, the energy storage device in the one or the other working range. The result is that for the case that the vehicle is to be started by the high voltage energy accumulator it is possible to guarantee a reliable start of the internal combustion engine even at low temperatures (cold start).
In addition, the intent is to carry out the shift of the working range as a function of the current operating mode of the vehicle (type of vehicle operating mode). In this case it is advantageous for a shift to occur as a function of which one of at least two different vehicle operating modes is currently on hand. In particular, a distinction is made between an engine start (start of the internal combustion engine), driving by just the electrical means, driving by just the internal combustion engine, a propulsion by the electric motor (motor driven) together with the internal combustion engine and a boost mode (call on maximum possible driving torque).
Analogous to the described method, there is provided an energy supply device which is intended for a hybrid vehicle (in particular, for a hybrid vehicle that can be operated electrically and/or by an internal combustion engine) and which comprises a high voltage energy storage device and a control unit for controlling the charging and discharging events of the energy storage device. In this respect the control unit is designed in such a manner that a predetermined working range of the high voltage energy storage device that is defined by an upper limit and a lower limit can be shifted as a function of the vehicle operating parameters and/or as a function of the vehicle environmental parameters.
The control unit is designed advantageously in such a manner that the shift is carried out by just shifting the lower limit of the working range. In another preferred embodiment the control unit can also be designed in such a manner that the working range is shifted in its entirety in one direction. That is, the upper limit and the lower limit are shifted in one and the same direction while at the same time retaining their distance and/or the range defined by said limits (or the charge quantity defined by them).
The high voltage energy storage device comprises energy storage elements, which are made advantageously on the basis of lithium ion technology. The control unit is designed advantageously in such a manner that the charging and discharging procedures of the high voltage energy storage device take place as a function of its state of ageing and/or as a function of the outside and/or vehicle ambient temperature.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.